Coolant overflow hose

[lurice0]

2001 Mazda Tribute

Why doesn't the coolant overflow hose connect to anything?
and what do i do with it during a pressure test?
and if the coolant system is truly a pressurized system, why is that hose not connected to anything? Why would the coolant cap have a pressure rating if the overflow hose is always open to air?

I know on my 95 civic i don't remember but i think i have to plug the coolant overflow reservoir during pressure tests. The overflow reservoir on the 95civic is also not completely sealed so i guess it's just i don't have a great understanding of that if someone could explain the relationship between the cap and overflow opening. For example how could the reservoir possibly explode, as i have seen happen, if the overflow hose is always open to air?

 

[SparkYellow]

My understanding is that the overflow tank is the same thing as the reservoir. The radiator (under the cap with the PSI rating) becomes pressurized when the car is running. When coolant in the radiator expands and reaches a certain pressure, the cap allows the excess to enter the overflow. When the engine is off and the pressure drops, the radiator will draw coolant back from the overflow to maintain the level in the radiator.

The open hose on the overflow is to allow fluid to enter and exit freely. Just like how we remove the oil cap when draining the oil to allow free flow (no vacuum/suction). It also prevents overflow from the overflow.

The cooling system is designed differently in different makes/models. On my MINI, there's no separate cap on the radiator itself. The overflow tank is pressurized. In that case, it can explode if it was overfilled.

 

[SparkYellow]

Ideally the open hose on your overflow tank should point downward. If you keep the level below max in the overflow, there shouldn't be any excess coming out of it.